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Estimation of the effect of future changes in precipitation in Japan on pluvial flood damage and the damage reduction effect of mitigation/adaptation measures [1]

['Hayata Yanagihara', 'Department Of Civil', 'Environmental Engineering', 'Graduate School Of Engineering', 'Tohoku University', 'Sendai', 'Miyagi', 'So Kazama', 'Tsuyoshi Tada', 'School Of Systems Engineering']

Date: 2022-08 

This study estimated the effect of changes in the amount of precipitation associated with climate change on pluvial flood damage and the effectiveness of mitigation and adaptation measures throughout Japan. First, the cost of damage caused by pluvial flooding was calculated based on extreme rainfall, assuming a situation in which river levels are high, and rainwater does not drain into the rivers. Additionally, extreme rainfall in future climates was estimated from the output values of five general circulation models. Then, using these figures for extreme rainfall, the cost of pluvial flood damage in future climates was estimated. Improving the maintenance level of inland water drainage facilities and converting buildings to a piloti design were selected as adaptation measures. The results showed that in the Representative Concentration Pathway (RCP) 8.5 scenario, the expected annual damage cost (EADC) in the late 21st-century climate (2081–2100) scenario increases to approximately 2.3 times that of the baseline climate (1981–2000). If climate change is mitigated to RCP 2.6, the EADC in the late 21st-century climate scenario is estimated to be reduced by 28% compared to the EADC in the RCP 8.5 scenario. It is also estimated that the EADC in future climates could be kept lower than in the baseline climate by taking multiple rather than single measures. However, in the RCP 8.5 scenario for the late 21st-century climate, even if multiple adaptation measures are taken, the EADC was estimated to increase by 9% compared to the EADC in the baseline climate.

Funding: This research was performed by the Environment Research and Technology Development Fund (JPMEERF20S11813, SK) of the Environmental Restoration and Conservation Agency of Japan. This research was supported by JHPCN (jh210001, SK), Joint Usage / Research Center for Interdisciplinary Large-scale Information Infrastructures. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Introduction

In 2015, the United Nations Sustainable Development Summit was held, and the outcome document “Transforming our world: the 2030 Agenda for Sustainable Development” was adopted [1]. In this agenda, Sustainable Development Goals (SDGs) comprising 17 goals and 169 targets were identified. One of these SDGs was to “take urgent action to combat climate change and its impacts.” Additionally, in “The Global Risks Report 2021,” failure to adapt to climate change was ranked among both the global risks with the highest likelihood of occurrence and the global risks with the highest impact [2]. These statements reflect the fact that adaptation to climate change has become a global priority.

On global warming, the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) states that warming of the climate system is unequivocal [3]. In addition, it is predicted that climate warming will change the amount of precipitation in Japan. Fujita et al. (2019) [4] showed that, unless additional mitigation efforts are made, statistically significant increases, not only in annual average daily precipitation but also annual maximum daily precipitation, may occur in mid- and high latitude regions, including Japan, in the near future (between 2030 and 2050). Hatsuzuka and Sato (2019) [5] suggested that extreme monthly precipitation with a return period of 100 years between June and August would increase in many parts of Japan due to global warming. Nayak and Takemi (2020) [6] applied a pseudo-global warming experiment to four typhoons that made landfall in northern Japan in August 2016 and showed that three of these typhoons could cause more rainfall in the north under future climate conditions. These studies suggest that flood damage will become more severe in the future. Further, since precipitation is predicted to increase even before the end of the 21st century, it is necessary to consider adaptation to flood damage given the rainfall increases associated with climate change. In considering specific adaptation measures, it is necessary to evaluate the flood risk and the effectiveness of the adaptation measures quantitatively.

Multiple flood assessments have been done in many countries around the world. On a global scale, Winsemius et al. (2013) [7] proposed a framework for assessing the global risk of river flooding that could also be applied to future scenarios. Arnell and Gosling (2016) [8] used multiple climate models to evaluate the impact of climate change on flood frequency, exposed population, exposed cropland area, and flood risk indexed by average annual flood loss. Dottori et al. (2018) [9] evaluated human losses, direct economic damage, and indirect welfare losses due to river flooding associated with global warming. As an example of a flood risk assessment targeting Japan, Kazama et al. (2009) [10] estimated the cost of flood damage throughout Japan, assuming flood protection facilities suitable for a 50-year return period flood. Tezuka et al. (2014) [11] evaluated the impact of climate change on the cost of flood damage throughout Japan. These studies mainly focused on flooding from rivers (fluvial flooding). However, a lack of research on the risk assessment of pluvial flooding has been identified [12,13].

In Japan, following damage caused to many homes in eastern Japan by pluvial flooding resulting from Typhoon Hagibis in 2019 [14], the importance of taking measures against pluvial flooding has grown. On a city scale, pluvial flooding risk assessments [15–18] and climate change impact assessments [19–21] have been conducted. Several assessments of pluvial flooding targeting large areas, such as entire countries, have also been carried out [22,23], but these are few compared with the number of studies on a city scale. For this reason, there is insufficient knowledge about the spatial distribution of pluvial flooding risk throughout Japan taking account of climate change. Climate change impact assessments for entire countries are useful for identifying areas in which the importance of measures against pluvial flooding is increasing. On adaptation measures, evaluations of adaptation measures against pluvial flooding have been conducted on a city scale [24–26]. Meanwhile, evaluations of adaptation measures against river flooding have been conducted on a global and national scale [27,28]. However, no studies have examined the effectiveness of adaptation measures against pluvial flooding targeting entire countries, including Japan. Evaluating adaptation measures for an entire country makes it possible to discuss the adaptation measures needed to reduce the impact of climate change by region.

This study estimated the effect of changes in the amount of precipitation associated with climate change on pluvial flood damage and the damage reduction effect of pluvial flooding adaptation measures throughout Japan. In addition, it also evaluated the pluvial flood damage reduction effect due to mitigation measures. It is hoped that the results obtained in this study will be useful in predicting future changes in pluvial flood damage and examining the effectiveness of adaptation measures.

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[1] Url: https://journals.plos.org/climate/article?id=10.1371/journal.pclm.0000039

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